Histone post-translational modification (PTM, or histone mark) is critical to dynamic modulation of chromatin structure and function. Dysregulation of histone modification processes contributes to the development of many diseases, such as cancer, cardiovascular and neurological diseases. We recently reported a new, evolutionarily-conserved histone mark, lysine 2-hydroxyisobutyrylation (Khib). We showed that Khib is present among 63 histone lysine residues in both human and mouse, more than the known numbers of the widely studied histone acetylation (Kac) and methylation (Kme) sites. We also obtained multiple lines of evidence that suggest important and unique biological functions of histone Khib: this class of histone modification shows distinct genomic distributions from the widely studied histone Kac during male germ cell differentiation; it is associated with active gene transcription and H4K8hib is a better indicator for high gene expression than its corresponding H4K8ac; histone Khib can direct in vitro transcription in a manner dependent on 2-hydroxyisobutyryl CoA, suggesting that histone Khib impacts chromatin structure and transcriptional activity; histone Khib has different profiles between transcriptionally active and transcriptionally silent chromatin in Tetrahymena thermophile, in different cell cycle stages, and during mouse spermotogenesis. These results suggest that histone Khib is structurally and mechanistically different from histone Kac. The major players regulating histone Khib pathway would break new ground in epigenetic research and improve our understanding of cellular physiology and human disease. In the proposed research, we will study histone Khib pathway using an integrated approach. We will identify histone Khib-regulatory enzymes and direct binding proteins of histone Khib marks. We will also investigate genomic distributions of key histone Khib marks in mouse genome, and compare these data with those of the well-studied histone acetylation and methylation marks. Our team is well positioned to carry out this project, because of our extensive expertise in the areas of epigenomics, biochemistry, proteomics, stem cell biology, and the tremendous preliminary results we generated. This study will overcome a major hurdle to study biology of histone Khib pathway by revealing key regulatory elements and likely characterize novel epigenetic mechanisms, perhaps analogous to the characterization of histone Kac and Kme pathways.